The present invention relates generally to an optical transceiver, and more particularly to a receiver optical subassembly with an adjustable bandwidth transimpedance amplifier in an optical transceiver.
Optical transceivers are often used in optical communication systems. Optical transceivers transmit and receive optical information generally at very high data rates. In many applications the optical information is formed by modulating light from a laser, either by direct modulation of the laser or by using a separate modulator, such as an electroabsorbtion modulator or a lithium niobate modulator. The modulated light is passed over a fiber optic line, often simultaneously with light from other lasers at varying wavelengths, and received by a receiver.
The receiver detects the received light, generally using a photodetector such as a photodiode. The photodetector converts the received modulated light signal to an electrical signal. Electrical signals produced by photodetectors are generally very small current signals. Transformation of the current to a voltage and amplification of the voltage is generally performed to provide a signal which may be used by further downstream electrical processing components. Amplification of the signal is often problematic as the amplification often distorts and adds noise to the signal.
Transimpedance amplifiers are often used to convert the small current signal provided by the photodetector into an amplified voltage. Transimpedance amplifier design often involves a number of trade-offs, where improvement in one area results in degradation in another. For example, improvement in output signal quality may sometimes be achieved by limiting the useful bandwidth of the device. Accordingly, often transimpedance amplifiers are optimized for a specific bandwidth. Unfortunately, the use of a transimpedance amplifier optimized for a specific bandwidth generally implies that a receiver unit using the transimpedance amplifier may only be used in a system receiving data approximate the specific bandwidth. However, optical communication systems may provide data at a number of different data rates. Therefore, different receiver units with different transimpedance amplifiers are often required for the different data rates available for optical communication systems. This reduces flexibility in the use of receiver units and increases inventory stocking costs.